This invention relates to an improvement in performance of a storage system, and more particularly, to a technology for controlling queuing of I/O commands to realize optimal performance.
In a storage system, upon reception of an I/O command from a host computer, data is written in or read from a disk drive according to the I/O command. When the storage system receives a next I/O command before the execution of the I/O command is finished, the received I/O command is temporarily stored in a FIFO type memory to wait for execution. Storing of one or more I/O commands in the memory to wait for execution as described above is called queuing of I/O commands. When a plurality of I/O commands wait for execution, the I/O commands may be rearranged to be executed in an order different from the received order, which may shorten time necessary for execution. For example, JP 06-259198 A discloses a technology for rearranging I/O commands such that head seek time or rotational delay of a disk drive can be minimum, to thereby shorten execution time of the I/O commands.